The GPS system has achieved enormous popularity with both military and civil users. The system has evolved with its increased acceptance, with advances in GPS receiver technology allowing smaller, more accurate receiver units to be provided. Initially, global positioning systems were confined mainly to vehicles. As the technology has become more widely accepted, however, GPS receivers have been implemented in a number of different environments, each with its unique demands. For example, GPS receivers have been implemented into handheld devices, allowing users to utilize GPS navigation away from their vehicles. These handheld devices have found application in military, recreational, law enforcement and civilian search and rescue applications. Some of these devices also include communications capability for wireless communication with similar units or a central location.
In most applications, it is desirable to maintain consistent periodic estimates of a device's location, both to provide timely aid to the user in navigation and to report a reasonably precise position at a point in time to an oversight/management location. A GPS system must also monitor available almanac and ephemeris data to maintain the ability to obtain a position fix from visible satellites in a reasonable amount of time. This presents little trouble in vehicle implementations, as they generally have access to a large-capacity power supply, but can be problematic in handheld units, which generally have a relatively limited power supply; this problem is compounded when the device includes communications equipment drawing on the same power supply. Current implementations are so inefficient that carrying spare batteries for an entire week of GPS/communications operations would be infeasible for most users.
The fundamental problem with current implementations involves limitations in the present art of how electronic communications are implemented in handheld systems. Weight, size, and battery life are significant design drivers for communications devices designed to carried by an individual (e.g., in the hand, in a backpack, or attached to the body by some other means, such as slung from the belt). This problem is compounded by the fact that the very applications where dismount communications are most useful are those where the weight and size of the communication device are of the most concern. Reducing the power consumption of a GPS receiver without compromising its accuracy or efficiency is therefore desirable.